It is these days common, and even a legal requirement, for certain types of container, such as pill boxes (that is to say, containers of pharmaceuticals or medicaments generally in solid dose form, such as pills or pellets), to be secure. More specifically, they should be child-proof (a term that usually means child-resistant) in that they must be difficult, and even impossible, to open, by a simple operation.
One known type of security container requires the (screw-on) lid to be pressed firmly down/on before it is unscrewed, while another requires the lid to be correctly aligned before it can be prised off. However, a press-down lid may be very difficult for the aged or arthritic to operate, while the most common container requiring alignment (of respective marks on the lid and on the container body) may be too easily opened by an intelligent child.
U.S. Pat. No. 4,535,903 describes a security container in which the lid includes a retractable member. When retracted, there is no evident means of opening the lid; manipulation of the member, through a window in the lid, allows it to be pushed out from the lid, only then providing an evident tab, for opening the lid. Although this device should be easy to operate without it being readily evident how it can be opened, it suffers from several practical disadvantages. These disadvantages include ease of opening, e.g. by a child using teeth, or accidental opening, even when the retractable member is retracted, and the difficulty of balancing ease of retraction/opening, e.g. for the infirm or those with large fingers, with desired security. Further, a bulky lid is required, especially if the retractable member is to be adequately durable, with attendant problems of plastic shrinkage, and difficulty in moulding and manufacture, e.g. non-suitability for ultrasonic welding. This also means that the container must be sufficiently large that it will not generally be considered portable.